This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-091021, filed Mar. 29, 2000, the entire contents of which are incorporated herein by reference.
The present invention relates generally to a cathode ray tube apparatus, and more particularly to a cathode ray tube apparatus incorporating an electron gun assembly capable of compensating dynamic astigmatism.
A color cathode ray tube apparatus, in general terms, comprises an in-line electron gun assembly for emitting three electron beams, and a deflection yoke for generating deflection magnetic fields, thereby deflecting the electron beams emitted from the electron gun structure and horizontally and vertically scanning them over a phosphor screen. The deflection yoke forms a non-uniform magnetic field by generating a pincushion-type horizontal deflection magnetic field and a barrel-type vertical deflection magnetic field.
The electron beams, while passing through the non-uniform magnetic field, are affected by a deflection aberration, i.e. astigmatism in the deflection magnetic fields. Consequently, the beam spots of electron beams landing on peripheral portions of the phosphor screen are distorted, and the resolution deteriorates. Jpn. Pat. Appln. KOKAI Publication No. 64-38947 discloses a dynamic focus type electron gun assembly as means for solving the problem of deterioration in resolution due to deflection aberration.
FIG. 10 shows this electron gun assembly having a main lens ML. The main lens ML is composed of a dynamic focus electrode G5, to which a dynamic focus voltage Vd is applied, an anode G6, to which an anode voltage Eb is applied, and auxiliary electrodes GM1 and GM2 disposed therebetween. Voltages obtained by dividing the anode voltage Eb by means of a resistor 100 disposed near the electron gun assembly are applied to the auxiliary electrodes GM1 and GM2.
Thus, asymmetric lenses QL1 and QL2 are formed, respectively, between the dynamic focus electrode G5 and auxiliary electrode GM1, and between the auxiliary electrode GM2 and anode G6. As the electron beams are deflected toward the peripheral portion of the phosphor screen, the dynamic focus electrode G5 is supplied with the dynamic focus voltage Vd and the asymmetric lens QL1 performs a diverging function only in the vertical direction, without performing a lens function in the horizontal direction.
With these lens functions, this electron gun assembly corrects the distortion of electron beam spots on the peripheral portion of the phosphor screen.
In this electron gun assembly, however, since the dynamic focus voltage is applied to the dynamic focus electrode G5, a capacitance is created among the electrodes of the main lens ML, and due to the capacitance, part of an AC component of the dynamic focus voltage is superimposed on the voltages applied to the auxiliary electrodes GM1 and GM2. As a result, the asymmetric lens QL1 created between the dynamic focus electrode G5 and auxiliary electrode GM1 has a deficient lens action, and the asymmetric lens QL2 created between the auxiliary electrode GM2 and anode G6 has an undesirable lens action.
Accordingly, distortion of the beam spot on the peripheral portion of the phosphor screen cannot fully be corrected, and it is difficult to obtain good focus characteristics over the entire phosphor screen.
In a case where the main lens ML includes, as shown in FIG. 10, two or more auxiliary electrodes (GM1 and GM2) supplied with voltage from the resistor 100 disposed near the electron gun assembly, it is disadvantageous, in terms of breakdown voltage, to dispose voltage supply terminals 110 and 120 in a near position on the resistor 100.
Where voltage supply lead wires for supplying voltage to the auxiliary electrodes GM1 and GM2 are to be led out of the resistor 100, it is preferable for the purpose of easier work to dispose the voltage supply terminals 110 and 120 of the resistor 100 near the auxiliary electrodes GM1 and GM2. As a result, where there are two or more auxiliary electrodes (GM1 and GM2), the two or more voltage supply terminals (110 and 120) are positioned close to each other on the resistor 100.
In this case, an electric discharge will easily occur between the two or more voltage supply terminals (110 and 120) and a problem of breakdown voltage may arise.
In order to solve this problem, in an electron gun assembly as shown in FIG. 11, a second auxiliary electrode G6 is disposed away from the first auxiliary electrode GM1, that is, between two focus electrodes G5 and G7. The second auxiliary electrode G6 is connected to the first auxiliary electrode GM1 and is supplied with voltage from a voltage supply terminal on the resistor 100 disposed near the secondary auxiliary electrode G6. Accordingly, the distance between the voltage supply terminal 110 for voltage supply to the first auxiliary electrode GM1 and second auxiliary electrode G6 can be located sufficiently away from the voltage supply terminal 120 for voltage supply to the auxiliary electrode GM2. Thus, a problem of breakdown voltage can be solved.
Even with this structure, however, it is necessary to additionally provide the electron gun assembly with the second auxiliary electrode G6, and the total number of electrodes of the electron gun assembly increases, resulting in an increase in cost. Moreover, the number of electron lenses formed within the electron gun assembly increases, and an error tends to occur in the trajectories of electron beams.
In the structure of the prior-art electron gun assembly, as described above, an AC component of the dynamic focus voltage is superimposed on the voltage applied to the adjacent electrode, and the electron lens formed by these electrodes causes an undesirable lens action. It is thus difficult to satisfactorily correct the distortion of the beam spots of electron beams deflected onto the peripheral portions of the phosphor screen.
Moreover, with the prior-art electron gun assembly, where the two or more auxiliary electrodes supplied with a part of anode voltages divided by the resistor are disposed close to each other, the voltage supply terminals on the resistor are also disposed close to each other. This is disadvantageous in terms of breakdown voltage.
Furthermore, in order to eliminate the disadvantage on breakdown voltage, the structure may be adopted wherein a second auxiliary electrode is additionally disposed away from a plurality of closely-arranged first auxiliary electrodes, one of the first auxiliary electrodes is electrically connected to the second auxiliary electrode, and the voltage supply terminals are provided on the resistor disposed near the second auxiliary electrode. In this case, however, the total number of electrodes of the electron gun assembly increases, resulting in an increase in cost. Besides, the number of electron lenses formed within the electron gun assembly increases, and an error tends to occur in the trajectories of electron beams.
Consequently, the focus characteristics deteriorate over the entire phosphor screen, and it is difficult to obtain well-shaped beam spots.
The present invention has been made in consideration of the above problems, and the object of the invention is to provide a cathode ray tube apparatus wherein a disadvantage on breakdown voltage is eliminated and well-shaped beam spots can be formed over an entire phosphor screen without increasing manufacturing cost.
In order to achieve the object, a cathode ray tube apparatus according to claim 1 comprising:
an electron gun assembly including an electron beam generating section for generating at least one electron beam, and a main focus lens section for focusing the electron beam on a screen; and
a deflection yoke for generating deflection magnetic fields for deflecting and scanning the electron beam from the electron gun assembly on the screen in horizontal and vertical directions,
wherein the main focus lens section comprises at least one focus electrode, to which a fixed focus voltage of a first level is applied, at least one anode to which an anode voltage of a second level higher than the first level is applied, at least one first auxiliary electrode to which a voltage obtained by resistor-dividing the anode voltage via a resistor and having a third level higher than the first level and lower than the second level is applied, and at least one dynamic focus electrode to which a dynamic focus voltage obtained by superimposing on a focus voltage an AC voltage varying in synchronism with the deflection magnetic fields generated by the deflection yoke is applied,
the main focus lens section includes an ultimate main focus lens section composed of the dynamic focus electrode, the at least one first auxiliary electrode and the anode, which are arranged successively in a direction of travel of the electron beam, and at least one second auxiliary electrode connected to the first auxiliary electrode is provided on the electron beam generating section side of the ultimate main focus lens section, and
an electrode to which a fixed voltage is applied is disposed near the second auxiliary electrode such that an induction voltage induced in the first auxiliary electrode of the ultimate main focus lens section may be reduced.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.